1. Field of the Invention
This invention relates to plate-fin type heat exchangers, and particularly to a novel construction of the closure bars. More specifically, the closure bars are formed of solid material and shaped in a manner which provides at the corners or along the length of the heat exchanger core a straight continuous protruding flange to which headers may be welded, thereby avoiding welding of the headers directly to the core. The construction is advantageous in that welding of the headers may be automated, damage to the core due to the welding is avoided, and damage caused by thermal cycling of the heat exchanger is reduced.
2. Description of the Prior Art
Plate-fin type heat exchangers with various fluid flow patterns are well known in the art, and consist of a core formed from stacked layers of continuous corrugated fin elements. Each layer is mounted so that the channels formed by the fins in one layer lie in transverse or parallel relation to the channels formed by the fins in adjacent layers whereby fluid flow passing through the channels is in cross-flow or counterflow relation in alternate layers. A parting sheet is placed between adjacent fin layers to maintain separation between alternate fluid flow paths, and top and bottom cover sheets are also required for structural support. Closure bars are mounted on the core sides to act as seals, the closure bars on each side being located on alternate layers and parallel to the channels to form a structure in which a first fluid passes through alternate layers of the core in one direction and a second fluid passes through the remaining layers in a direction perpendicular or parallel to the first fluid. A typical heat exchanger construction is shown in U.S. Pat. No. 3,265,129 assigned to the assignee of this application.
To direct the fluid flow into the channels, headers are normally welded to the core at the fluid inlet side, or the fluid outlet side, or commonly both sides. Usually headers are welded to the corners of the core where most of the structural loads are applied. Since the core including the fins, parting sheets and closure bars are normally joined by brazing, welding the headers directly to the core has, in the past, created problems because welding occurs typically at a temperature of about 2,000.degree. F. (1109.degree. C). Often the core is distorted and the braze alloy flows due to the high welding temperature, necessitating repair of the core in many instances.
One attempt to solve this problem is the use of core bands welded to the square corners of the core, and the headers are in turn welded to the core bands. Where high pressures or structural loads have to be transmitted to the core, the weld area required is large and a square corner does not allow sufficient weld area. In some applications the closure bars are bent 90.degree. around the corner to allow added weld area, but this structure blocks parts of the core adjacent to the extended bend of the closure bar, and the flow area is reduced resulting in degraded core performance. U.S. Pat. No. 3,265,129 attempts to solve the problem by bending the closure bar less than 90.degree. at the corners so that when the core is stacked, the mitered bends are aligned such that they form a continuous solid area at the corners to which the headers can be welded with or without the use of core bands. This latter approach is still subject to core damage when the headers are welded, and some of the core flow area is lost, although less than bending the closure bars 90.degree..
The present invention overcomes the deficiencies of the prior art and provides a heat exchanger closure bar construction which avoids welding the headers directly to the core, and in fact removes the welding area from the core itself.
It is therefore an object of this invention to provide an improved heat exchanger construction.
Another object of this invention is a heat exchanger in which the headers are welded to a continuous solid flange member formed by the closure bars at a location adjacent the core corners or along the length of the core where the welding will not damage the core.
A further object of this invention is a heat exchanger in which the welding of headers thereto is easily automated.
A still further object of this invention is a heat exchanger which provides an intermediate member between the header and the core thereby permitting less strain from the header due to thermal cycling of the core and leading to less cracking of the header-to-core joints.